Field of Endeavor
The present invention relates to apparatuses, systems and methods for improved boat of both mono-hull and multi-hull designs. More particularly, the invention relates to boat hulls having a keel configured as an inverted foil providing better fuel economy, maneuverability, a smoother ride at both high and low speeds, less side to side rolling motion when stationary in waves and greater weight carrying capacity.
Background Information
Boat hull design has been a constantly evolving field of art for thousands of years. In particular, the development of non-wind propulsion systems, material science and other technologies, has contributed to many advances in hull design over the past two hundred years.
Flat-bottom boats have a large, substantially flat hull bottom, making them very stable in calm weather. Characteristically, however, the flat, broad bow area creates a rough ride. These boats are usually limited to low horsepower motors because they do not generally handle well at high speed. Flat-bottom boats are also well suited for shallow water.
Early in nautical history, boats were powered by wind or by hand-stroked oars. Early boat designers found that boats went faster, and were easier to steer, if the bow was pointed. They also soon discovered that by lowering the center of gravity, the sailing boats had better stability, and usually kept the boat upright even in bad weather.
With the advent of mechanical power came boats with “planing” hulls, which lift the boat partially out of the water to skim on the surface allowing the boat to be operated at higher speeds for the same power. “Displacement” hulls push through or cruise through the water instead of skimming on the surface and are not able to operate at the higher speeds of a planing hull.
“Semi Displacement” hulls act in a manner part way between Displacement hulls and Planing hulls. At slow speeds they are more efficient than Planing hulls but not as efficient as Displacement hulls, while at medium speed they are more efficient than both Displacement and Planing hulls. Semi Displacement hulls are not usually able to operate at the high speeds typical of Planing hulls but are able to operate efficiently at higher speeds than a Displacement hull.
The V bottom boat is probably the most common hull design for planing hulls. Most manufacturers of performance boats built today use variations of this design. This design offers a reasonable ride in rough water as the pointed bow slices through the water forward and the V-shaped bottom softens the slamming of the boat in waves. The angle of the V is called “deadrise”. A sharper V has more deadrise. Some “V”-bottom boats have a small, local flat surface at the very bottom of the aft end called a “pad.” This pad creates a little more lift which increases top speed but at the sacrifice of a little softness in the ride. Typically, a V hull boat has no real keel, simply a sharp angle at the bottom point of the V.
A chine in V bottom planing or semi-displacement power boat hull forms refers to the hard corner or edge at the intersection between the hull bottom and the hull side.
With sailboats, it is common to have a rounded hull with no strakes or chines. A keel is often employed. However, the keel of a sailboat generally is generally deep vertically in proportion to the overall depth of the hull. On modern designs, it does not typically run the length of the boat.
Boats having a flatbottom, are stable at low speed while also being maneuverable and provide a large displaced volume for a given draft, thus accommodating more weight. Flatbottom boats typically have no keel.
A deep V hull provides a relatively smooth ride at high speed. However, at low speed a deep V hull is very inefficient. Furthermore, at low speeds, a deep V hull is less stable, less maneuverable and tends to roll side to side to a high degree when side on to the waves.
Many attempts have been made to design hulls that combine features of flatbottom, round and/or deep V hulls in an effort to design hulls exhibiting the advantages of each.
The purpose of a keel, fin, or centerboard is to provide resistance to making leeway; in effect, to keep the yacht from sliding sideways through the water due to wind pressure on the sails. Various shapes of underwater plane have been in and out of style over the past 150 years. Keels are generally not considered particularly necessary for powered boats, including V hull boats because they are not subject to the lateral forces caused by wind against a sail, there is also no need to use a keel for counteracting these forces to stabilize a boat. Nonetheless, keels have from time to time been incorporated into various powered boats.
The deep, full keel has been used since at least the mid-1800s for the shoal-water areas by centerboard craft. These cover such working types as the sharpies, Cape Cod catboats, Chesapeake Bay oyster skiffs and the like.
Until the mid 20th century, typical offshore yachts keels similar to those of a sailing fishing craft. They had a long, full keel with deep forefoot and fairly vertical sternpost. This shape provides directional stability, ease of steering, and the ability to heave to in heavy weather. However, these keels also resulted in slowness in stays, excess wetted surface and an inefficient lateral plane shape that has excess leeway.
To overcome these deficiencies, a modified full-keel form was designed which provided generally good handling and directional stability plus reduced wetted surface, compared to a true full-keel. The yachts can perform well in all conditions and, as they are generally of heavier displacement than contemporary ballasted-fin boats, they do not give away much in light air, despite the added wetted area.
Modern keels are generally designed in a manner similar to those of airplane wings. The maximum thickness of the keel is usually recommended to be located about 35% of the aft of the leading edge. In addition, the leading edge should be elliptical with the trailing edge slowly tapering to a point. This is in keeping with the standard designs of airfoils. It has become the industry standard to use keels having a foil-based design according to NACA standards.
In view of the foregoing, there is a need to provide a hull design that performs well at both high and low speeds. It is therefore desirable to provide a hull combining improved performance and ride comfort of any of the existing hulls at speed and in waves and improved comfort of any of the existing hulls at slow speed in waves and when stationary in waves.